To make sterling silver, 92.5% silver is alloyed with other alloys, such as 7.5% copper. While this results in sterling silver, the resulting alloy is relatively soft and tarnishable. As many will attest, conventional sterling silver tarnishes readily, and must typically be polished before use. The properties of sterling silver can be enhanced by increasing the hardness of the alloy, by making the hardness of such alloy reversible, and by providing enhanced tarnish resistance.
U.S. Pat. Nos. 4,810,308 and 4,869,757 discuss silver alloys with reversible hardness. However, these alloys contain high amounts of copper, and their tarnish resistance is not much better than that of conventional sterling silver alloys.
U.S. Pat. No. 4,973,446 discusses certain silver alloys that are designed to reduce fire scale. However, they only contain about 0.5% copper, and do not appear to show reversible hardness characteristics.
U.S. Pat. No. 5,037,708 broadly teaches that silver alloys may contain substantial amounts of palladium, which significantly increases the cost of the alloy.
U.S. Pat. No. 5,039,479 discloses silver alloys that contain no lithium, and are generally low in copper. The amount of copper is typically less than about 2.6%. These alloys do not exhibit desirable hardening characteristics.
U.S. Pat. No. 5,558,833 discloses silver alloys that are based on solver-indium formulations, and do not provide desirable hardening properties.
U.S. Pat. No. 5,817,195 discloses silver alloys containing about 0.25%–0.5% nickel. Nickel-containing alloys are thought to cause allergenic reactions.
U.S. Pat. No. 5,882,441 discloses silver alloys have no tin and a low copper percentage, and therefore do not show desirable hardening properties.
U.S. Pat. No. 6,406,664 teaches certain silver alloys containing nickel, and that do not contain lithium.
U.S. Pat. No. 6,726,877 again teaches silver alloys with no tin and no lithium.
The foregoing prior art references are hereby incorporated by reference with respect to the technical background of this invention.